1. Field of the Invention
The present invention relates to an apparatus for supplying gases or the like for use in the production of semiconductors, chemicals, precision machine parts, etc. More specifically, this invention relates to a parallel divided flow type fluid supply apparatus so configured that when any one of a plurality of flow passages arranged in parallel is opened for fluid to flow, the effect of that operation on the flow rates in other flow passages is minimized.
The present invention also relates to a method of controlling the flow rates of various gases used in an apparatus for supplying gases or the like for use in the production of semiconductors, chemicals, precision machine parts, etc. More specifically, this invention relates to a fluid switchable pressure-type flow control method and a fluid switchable pressure-type flow control system (FCS) in which the flow of various gases can be regulated with high precision by one pressure-type flow control system on the basis of flow factors.
2. Background Art
So-called mass flow controllers are now used in almost all fluid supply apparatuses for manufacturing facilities of semiconductors or chemicals.
FIG. 14 shows an example of the prior art single flow passage-type fluid supply apparatus in which such material gases G are adjusted by a regulator RG from primary pressure to secondary pressure before being sent into the flow passage. The primary pressure is usually a relatively higher pressure and detected by a pressure gauge Po. The secondary pressure is a relatively lower pressure under which the fluid is supplied to the downstream flow passage. The secondary pressure is measured by a pressure gauge P1.
A mass flow controller MFC is installed between valves V1 and V2 for control of the flow. Also provided is a mass flow meter MFM to measure the flow rate. The material gas G is used for a treatment reaction or the like in the reaction chamber C and then discharged by vacuum pump VP through a valve VV.
This single flow passage-type supply apparatus presents no problem with the treatment reaction remaining stable in the reaction chamber C as long as the material gas G is supplied in a normal state with no external disturbances or changes in flow rate.
But a problem is encountered with an arrangement in which material gas G is supplied through one regulator and branched off into two or more flow passages. FIG. 15 shows an arrangement in which the flow of the material gas 6 from one regulator RG branches off to two flow passages S1 and S2. In practice, a reaction chamber (not shown) is also provided on flow passage S2 and is so arranged that gas reaction may proceed into the two reaction chambers. The same elements or components as in FIG. 14 are indicated by the same reference characters with different suffixes given for different flow passages. Those similar elements or components will not be described gain.
An experiment was conducted to study what effect the opening of oic closed flow passage would have on the flow of another opened flow passage. In the experiment, the material gas was supplied through flow passage S1 with valve V1 and valve V2 opened and a specific reaction proceeding in the reaction chamber C, while the flow passage S2 remained closed with valve V3 and valve V4 closed. Then, the valve V3 and valve V4 were opened to supply the gas into the flow passage S2 at a specific set flow rate by quickly actuating mass flow controller MFC2.
FIG. 16 shows the time charts of various signals. The instant the valve V3 and valve V4 were opened, MFC2 and MFM2 signals on flow passage S2 overshot to a high peak and then fell to a constant level.
The overshooting or the transient state caused the signals of MFC1 and MFM1 on flow passage S1 to change violently because of a change in pressures P1A, P1B.
This change in turn has an effect on the rate of reaction in the reaction chamber C. The external disturbance from flow passage S2 hinders a steady reaction in the reaction chamber C on flow passage S1. In the process of manufacturing semiconductors, this problem could cause lattice defects in the semiconductor. In is etching plasma, the process could be affected. In a chemical reaction, the oversupply or short supply of material gas G could cause finished products to change in concentration. This change could lead to unpredictable problems through “chaos phenomena.” However, little transient effect is wrought on upstream pressure Po. This is because of the presence of the regulator RG.
To eliminate the external disturbance indicated in FIG. 16, it is desirable to install regulator RG1 and regulator RG2 on the two flow passages S1 and S2 as shown in FIG. 17. The regulator RG2 could prevent the change in pressure from being felt on the upstream side when the flow passage S2 is suddenly opened. The steady supply of the fluid in flow passage S1 would not be affected. Conversely, the opening and closing of flow passage S1 would have no affect on the side of flow passage S2 
In this connection, the regulator RG is a device to convert the high pressure fluid into low pressure fluid ready for supply to the downstream flow passage. However, the pressure changing device is itself expensive.
The number of regulators RG needed would increase with the number of flow passages. That would make the whole of the fluid supply arrangement complicated and large, sending up the costs.
In the fluid supply apparatuses shown in FIG. 14 and FIG. 15, only one kind of gas is supplied. In practice, however, a plurality of kinds of material gases G are led into the reaction chamber C, one by one or simultaneously, in semiconductor manufacturing facilities.
It is also noted that the mass flow controller is used at almost all semiconductor manufacturing facilities or chemical production plants where the flow rate is required to be controlled with high precision.
FIG. 18 shows an example of the high-purity moisture generating apparatus for use in semiconductor manufacturing facilities.
Three kinds of gases—H2 gas, O2 gas and N2 gas—are led into a reactor RR through valves V1a-V3a with the flow rate controlled by the mass flow controllers MFC1a-MFC3a. The reactor RR is first purged with N2 gas with valve V3a opened and valves V1a, V2a closed. In the next step, the valve V3a is closed and valves V1a, are opened to feed H2 gas and O2 gas into the reactor RR. Here, H2 gas and O2 gas are reacted with platinum as catalyst to produce H2O gas. The high-purity moisture thus produced is then supplied to downstream facilities (not shown).
The problem is that each mass flow controller has its linearity corrected for a specific kind of gas and a specific low rate range. That is, the mass flow controller cannot be used for other than the kind of gas for which the controller is adjusted.
That is why the mass flow controllers MFC1a to MFC3a are installed for H2 gas, O2 gas and N2 gas, respectively, i.e., one mass flow controller for one kind of gas, as shown in FIG. 18. In a gas supply arrangement as shown in FIG. 18, furthermore, each of the mass flow controllers MFC1a to MFC3a is provided with a standby.
The mass flow controller is expensive and so are replacement parts. That increases the costs of gas supply facilities and the running costs.
Furthermore, if the mass flow controller is not replaced for a new kind of gas and, instead, the linearity is corrected every time a new gas is used, it takes long and it could happen that the operation of the manufacturing plant has to be temporarily suspended. To avoid that, it is necessary to have standby mass flow controllers for different kinds of gases ready in stock.
As set forth above, in case the flow passage from one regulator for regulation of pressure branches off into a plurality of parallel lines and each branch line is provided with a mass flow controller for regulation of the flow rate, then the opening of a branch line can cause a transient change to the other branch flow passages running in a steady state flow. This transient change in turn has an affect on the process in the reaction chamber off the branch line, causing a number of problems.
If each branch line is provided with one regulator to avoid such transient changes, meanwhile, that will make the fluid supply arrangement complicated and bulky, boosting the costs.
Furthermore, a large number of expensive standby mass flow controllers have to be stocked. That increases the costs of gas supply facilities and the running costs.
The present invention addresses these problems with the prior art.